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Advice needed - DIY off-grid solar electrics DC charging via AC from generator Answered

Hi all, new to this forum... I'm looking for some advice regarding an off-grid electrics setup i'm running. Currently i have a PV solar panel charging a battery bank through a charge controller. It's a 12vdc system. For 240vac i use a small (500W) inverter. For larger loads i use a diesel generator. The inverter is basic but very high quality sine wave, it doesn't do any charging nor does it automatically switch the load between the AC of the generator and its own AC (i do this manually). In order to recharge my batteries when there isnt enough sun (which is often!), i use a simple AC powered charger that isnt specifically designed for off-grid/solar applications. In other words it is not "intelligent" and doesnt have bulk, float or equalization settings - it's just a DC charger that gives decreasing current as the voltage of the batteries rises. In fact it is very prone to overcharging if left charging for too long and will keep putting current into the batteries even after they've reached 15.5vdc or more.

My question is this: is it a good idea to feed the DC charging current from my AC-fed charger into my solar charge controller in order to allow the charge controller to regulate and/or limit the charge as appropriate? I did this for a period of time and it seemed not to cause any problems. However, my AC charger did eventually blow its recrifying diodes although i'm not sure if this was due to a separate issue with the AC power coming from my generator which at the time was an old one and may not have been giving proper AC voltage (it may have been low due to engine speed problems).

The solar charge controller is a PWM type. The way i had it set up was the DC from the solar panel and the DC from the charger in parallel to the charge controller.

If there is no difference between the DC from the charger and the DC from the solar panel, i don't see how there could be any problem as it amounts to the same thing as having two 12v PV panels in parellel. However, what i dont know (due to insufficient technical knowledge) is whether rectified DC is any different to the DC from a solar panel.

My setup is as follows:
1 x 200W 12vdc PV panel
60A tristar PWM solar charge controller
2 x 6vdc Trojan t105 batteries wired in series to give 12vdc
Mastervolt 500w pure sine wave inverter (12vdc in, 240vAC out)
SDMO 6kva diesel generator (240vAC)
Wolf Max 50 battery charger (AC powered 40A DC charger)


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4 years ago

As a solar setup I have to wonder what you actually want to power with it.
If it is for something serious like your home I would upgrade a few things, if it just for a weekender or such I wonder about the generator.
All the small solar charge controller I had in my hands had three connections:
DC in
DC out
DC in can be fed by anything within the working rage of the controller like your solar panel.
DC out is for the load, e.g. your inverter.
And well battery speaks for itself I guess.

DC in and DC out are seperated by the protective electronics of the charge controller although in many cases they do share common ground.
If you want to use a common and simple battery charger with the charge controller that the best option is to use a switch to seperate the solar panel or to use a properly rated diode to make sure nothing is fed into the panel.
In general the voltage from the solar panel should be much higher than what the batteries need.
Unless your 12V panel actually gives around 16-20V you will have hard time charging.
Might be better to use 2 panels to get 24V input for the charge controller.


Reply 4 years ago

It is powering my "home" although my home is not a conventional house. I'm fully aware of all the upgrades i could (and would love to) make but unfortunately i dont have the money. I've managed to make this setup work for me for about 8 years, basically i'm just looking for some technical expertise in the area of electronics so i dont make DIY mistakes that will limit the life of my batteries/components. Unfortunately most of the advice readily available online is aimed at people doing things "by the book" which as i've explained i'm not in a financial position to do. If i had the money i would buy a xantrex (or similar) inverter/charger/AC changeover/generator start module, a huge solar array, wind turbine, water turbine and a bank of 2volt 1000 amp-hour cells.

I now know, through further research that rectified DC is not exactly the same as pure DC, since it has stray AC ripple within it (possible to control through use of capacitors and regulators) , although i'm still not sure if this would harm the charge controller or the charger.


Reply 4 years ago

If in doubt you can add one or more electrolytic capacitors of high value.
Something around the 20000µF mark to make sure the ripples DC comes out clean enough.
If you add the capacitors to the charger just measure the resulting DC voltage, it should be a little higher than what you measure without the capacitors and if that voltage is within the input range of the controller no harm will be done - if you secure the connection to the panel accordingly.